A hearing aid is an electronic device known to alleviate hearing loss of a human. Generally, the hearing aid captures sounds from the environment using one or more microphones and amplifies the captured sounds electrically according to a hearing aid prescription. Digital representations of the amplified signals are converted back into electrical signals suitable for driving an output transducer of the hearing aid for generating sound waves perceivable to its user.
Most traditional hearing aids are powered by single use (e.g., disposable) batteries or button cells such as zinc-air batteries. In fact, the sensitive electronics within these hearing aids are specifically designed for use with single use batteries. For example, the electronics are designed to accommodate or tolerate the voltages of single use batteries and discharge currents therefrom.
While single use batteries such as zinc-air batteries and other disposable batteries possess satisfactory energy densities and relatively inexpensive production costs, these batteries are single use, and once depleted, must be replaced. The hearing aid user must replace spent hearing aid batteries many times during the lifetime of the hearing aid. Thus, the advantage of a relatively low cost of a single hearing aid battery is lost because the battery must be replaced frequently, which aggregates battery costs. And, the small sizes of these batteries can make handling the batteries and replacing spend batteries in hearing aids difficult.
Rechargeable batteries or button cells offer the benefit of being rechargeable and reusable. However, the voltages or discharge currents from rechargeable batteries (e.g., silver zinc and lithium based batteries) are not compatible with the electronics in the hearing aids, because these electronics are designed for use with lower voltage single use batteries. For instance, common zinc-air hearing aid batteries typically include a maximum voltage of about 1.45 V under load, and a suitably sized rechargeable silver-zinc battery may possess a maximum voltage of about 1.86 V or greater under load. This maximum voltage corresponding to the rechargeable silver-zinc battery may exceed voltage thresholds of existing electronics within the hearing aid. Thus, the simple replacement of a single use battery with a suitably sized rechargeable battery risks damaging a hearing aid's sensitive electronics.